The field of the invention is mass transfer devices and the invention relates more particularly to devices that are constructed to pass a bulk fluid along the exterior surface of a plurality of hollow fibers. One such device is shown in U.S. Pat. No. 3,794,468. A porous cylindrical core is wound with a single length of capillary tubing as the core is being turned. A core insert directs the bulk fluid from the interior of the porous core over the exterior of the capillary tubes and out of the outlet tubes. A second fluid passes counter currently through the interior of the capillary tubes.
Another process for making a fiber bundle is shown in U.S. Pat. No. 4,572,446. Again, a bundle of hollow fibers are wound around a length of a core.
A similar design is shown in U.S. Pat. No. 5,299,749. Continuous lengths of filament are laid down on a core around a length of a core.
The flow of fluid within the hollow fibers and the fluid flowing on the outside of the hollow fibers is almost counter current. For some separation processes, it is beneficial that the flow be more across the axis of the hollow fiber rather than along the axis of the hollow fiber.